Installation of plaster board (sometimes referred to as "sheet rock") is a common operation in the construction of buildings. The operation typically involves the necessity to cut the board to an appropriate dimension. In remodelling operations, it is frequently necessary to cut out sections of plaster board from existing walls. The tool that is traditionally used for this operation is a reciprocating saw that inherently generates a large cloud of dust. The cloud of dust is a particular nuisance because of the unhealthy environment that it creates as well as the accumulation of dust. Operations carried out in homes or buildings that are occupied generally require that dust clothes be arranged over items such as expensive furniture or even floors to protect the items from the abrasive nature of the dust.
Numerous patents have appeared which disclose the use of various dust abatement schemes used with circular saws. These disclosures have generally been directed toward saws intended for use on wood such as the popular "Skill Saw.TM." which is constructed to cut panels such as wood panels which are more resistant to cutting than plaster board.
For example, U.S. Pat. No. 4,230,005 to Varga discloses a circular blade rotating in such a direction that its cutting edge enters into a guard casing at the cutting place, said guard casing having a rim closely adjacent to to the blade near the cutting place and pressed against the material being cut such as to prevent bending of the material.
U.S. Pat. No. 4,241,505 to Bodycomb et al discloses a dust shroud for a circular saw with two housings, one upper housing on the motor side of the panel being cut and a lower housing on the side of the panel opposite the upper housing with a flexible link aligned with the housings and aligned with the blade.
U.S. Pat. No. 4,253,362 to Olson discloses a guard casing enclosing a substantial portion of a circular blade canning a tube having one end connectable to a vacuum source and another end having a slot for accommodating a portion of the blade.
U.S. Pat. No. 4,255,995 to Connor discloses a dust tight housing for a table saw having a a rotatable shaft below the table.
U.S. Pat. No. 4,361,957 to Krotz et al discloses a chamber closely conforming to the cutting member (nibbler, drill bit, etc.) which is connected by a flexible hose to a vacuum chamber.
U.S. Pat. No. 4,411,067 to Kirk discloses a blade housing device for a cast cutting tool which is used to remove a cast from a patient, the housing having a wide periphery through which the a portion of the blade extends. The depth of the cut is preset and extension of the blade from the housing is fixed before the cutting operation. The housing is provided with a port for removal of dust by vacuum.
U.S. Pat. No. 4,414,73 to Pioch et al discloses a housing for a circular saw in which two handles are formed as an integral part of the housing and in which extension of the blade from the housing is preset before the cutting operation is performed.
U.S. Pat. No. 4,675,399 to Masanori et al discloses a circular saw with a sawdust collection system based on the generation of airflow from the rotating blade which transports the sawdust along a guide into a dust box.
U.S. Pat. No. 5,033,192 to Franx discloses a cutting or grinding disk with a hood through which a portion of the blade protrudes. The hood is equipped with a deflection baffle which directs the sawdust into an outlet stub.
U.S. Pat. No. 5,074,044 discloses a guard for a circular saw which has an impeller that rotates with the rotating blade and generates a suction with transport dust from the cutting region to a discharge outlet.
U.S. Pat. No. 5,121,543 to Onose et al discloses a portable circular saw having an upper blade guard with a discharge opening. A deflector within the guard directs the sawdust in a direction away from the operator.
U.S. Pat. No. 5,167,215 to Harding discloses a dust removal apparatus featuring a blade guard mounted for rotation on a side of the wheeled housing and a pivotally mounted funnel mounted on the blade guard. The funnel, telescopically mounted on the blade guard, extends between the blade guard and slab being cut. The funnel is provided with a bearing riding in contact with the slab. The funnel is connected to an exhaust duct leading to a vacuum source.
U.S. Pat. No. 5,327,649 to Skinner discloses a portable circular saw with a dust collector including an upper blade guard fixed to the motor and rotatably supporting the rotating blade and a lower blade housing that conforms to the extended cutting edge of the blade but which is hinged and folds back into the upper housing as the blade proceeds through the cut.
The job of cutting plaster board poses special problems that are not addressed by these disclosed examples of the prior art which are directed more toward the sawing of wood nor are they addressed by the "router" type of tool presently used for the purpose.
The plaster board, being made of cast plaster, disintegrates into a fine power when it is sawed so that it is very desirous to use a saw blade that is as thin as practical in order to minimize the amount of kerf that is generated by the cutting action. The reciprocating saw type blade inherently requires that a wide cut be made compared to a rotary saw so that a significantly larger amount of kerf is generated than could be achieved with a rotary blade.
Another problem is that, in carrying out many jobs such as in remodelling in which the board is nailed to a stud, the cutting blade encounters one or more nails such that the ordinary cutting blade such as a rotary blade or reciprocating saw is destroyed or at least degraded by such encounters.
Solution to the problem of a blade with sufficient impact resistance, suggesting the use of a very sturdy blade runs counter to a requirement for a very delicate blade in order to minimize the generation of kerf. A blade addressing both or these problems suggests that protection of the blade be provided at all times regardless of whether the saw is in use, momentarily set aside, or being stored or transported such as in a tool box along with other tools.
Another important consideration is that, often times, it is desirable to maintain a closely controlled depth of cut. This requirement occurs when the plaster board is nailed to a stud on the side of the board that is blind to the worker and his requirement is to cut out a section of board in which an edge of the section to be cut lies along the narrow side of a stud parallel to and spaced between the broad sides of the stud.
The reciprocating saw is not amenable to controlling depth of cut and its use often results in cutting unseen wires and plumbing.